Nothing special, just a picture of a bottle here.. iso 1600 with sony 50f1.8 on a tripod. Looks like the 580 missed focus, but the noise can be seen. 100% crops

-- hide signature --

-Matt

I downloaded the large files from your gallery and loaded them into LR 4. To be honest, I couldn't see much difference in the noise until I zoom in to about 300%.

To me, both appear to have about the same amount of noise, but the a77 has bigger noise pixels (slightly) and appears less smooth (more coarse). But, moving the noise reduction slider to the right on either image seems to have about the same affect. Both files seem to respond pretty well (for jpgs). Once you get past about 20, you start seeing a noticeable loss of sharpness / contrast.